Down
1 Essential piece of work, but not hard (4) CORE (CHORE - H)
2 Style of cooking soft roti infused with egg (8) TANDOORI (ROTI* with AND O) with on double duty? Part of 'infused with' and with=and?
3 A local group in French capital for those into drinking (6) PARISH (PARIS as pronounced by a drunk)
4 Sounded // positive (10) PRONOUNCED (2)
5 A treetop set for a drama (8) OPERETTA (A TREETOP)*
7 Rejected part of caesarian operation being broadcast (2-3) ON AIR (T<)
8 Theatre part including a box for management (13) ORCHESTRATION(ORATION including CHEST) I am unable to explain an R (CHEST in OR RATION) See comments
13 Small amount of money set apart in providing support (10) SHOESTRING(CD,DD) (SET* in SHORING)See comments
16 Act pulled off wearing fancy clothing (6,2) DOLLED UP (DO PULLED*)
17 Upcoming hospital department nurses to unite (8) EMERGENT (ENT nurses MERGE)
19 Sweet place for tea say? (6) AFTERS (Sweets come after the meal?) (AFTER S) See comments
21 It might get sticky to commit a second crime (5) RESIN (RE SIN)
23 Rodent seen in a central government school reportedly (4) CAVY (~KV=Kendriya Vidyalaya)

I don't think this was the setter's intention. Might be an inadvertent error.ORCHESTRATIONThis kind of mistake I have made too.When there are same two letters in parts when a disjunction is made, we are liable to make this error.The mind sees CHEST and ORATION but when proceeding to treat them, one R (at either end) is just missed out.Such errors can be/are caught only by repeated checking.

Brilliant work, Buzzer - thank you for a great time! Struggled a bit in the NE corner but it was a satisfying tussle. Great surfaces overall and some entertaining wordplay. 15a, 8d, 4d, 17d, and (especially) 19d were wow-inducing!

My only reservation is with the use of "one" for "un" in 24a, without any indication of the language shift.